The present invention relates in general to an electrophotographic imaging apparatus, and more particularly to systems and methods that compensate for time varying scan path errors in a multi-beam electrophotographic imaging apparatus.
In electrophotography, a latent image is formed by exposing select portions of an electrostatically charged photoconductive surface to laser light. Essentially, the density of the electrostatic charge on the photoconductive surface is altered in areas exposed to the laser beam relative to those areas unexposed to the laser beam. The latent electrostatic image thus created is developed into a visible image by exposing the photoconductive surface to toner, which contains pigment components and thermoplastic components. When so exposed, the toner is attracted to the photoconductive surface in a manner that corresponds to the electrostatic density altered by the laser beam. The toner pattern is subsequently transferred from the photoconductive surface to the surface of a print substrate, such as paper, which has been given an electrostatic charge opposite that of the toner.
A fuser assembly then applies heat and pressure to the toned substrate before the substrate is discharged from the apparatus. The applied heat causes constituents including the thermoplastic components of the toner to flow into the interstices between the fibers of the medium and the pressure promotes settling of the toner constituents in these voids. As the toner is cooled, it solidifies and adheres the toner image to the substrate.
In a conventional color electrophotographic imaging apparatus, such as a color laser printer, a color image to be printed is decomposed into cyan (C), yellow (Y), magenta (M) and black (K) color planes, which are developed and registered to form a corresponding composite toned image on a print substrate. Under this arrangement, the quality of the composite toned image printed onto the print substrate is affected by how accurately each color plane is registered to the remainder of the color planes. During the course of manufacturing such an apparatus, a registration process is typically performed to minimize the vertical (process) direction and horizontal (scan) direction registration differences between the CYMK color planes. Further, an operator may periodically implement a registration process to minimize the process direction and scan direction registration differences between the CYMK color planes, e.g., after new supplies are installed in the apparatus.
However, misregistration of one or more of the CYMK color planes may occur during normal operation of the apparatus, even in a precisely registered system, due to operational influences such as changes in temperature, humidity, etc. within the apparatus. For example, thermally induced expansion and contraction of optical components including lens elements can change their indicies of refraction, which can cause process and or scan direction shifts in a corresponding laser beam scan path relative to that beam's scan path at the time of a previous registration process.